Water-holding in skin is an essential factor for keeping the skin in good condition. So, a lot of cosmetics and pharmaceutical preparations which intend the moisturizing are sold in the market, and a lot of humectants are developed. Among of these, a hydrous oily component, e.g., cholesterol ester which is excellent in hydration property and moisturizing property, are used in particularly cosmetics.
However, in case of compounding such a hydrous oily component which was included a lot of water to the cosmetics, it had some problems in stability, since water was separated at a high temperature or temperature change with the passage of time.
Therefore, for keeping the stability of the cosmetics which comprising oil and water, various surfactants has been used in separately or by combining two or more as an emulsifier.
However, ionic surfactants such as alkyl sulfate and higher fatty acid salt has an apprehension of skin irritation, in the case where they are used at high concentration. And in case of using nonionic surfactants such as polyoxyethylene type, it has a problem in solubility such that nonionic surfactants inactivate an antiseptic such as paraben.
In order to solve these problems, it has been developed techniques which uses cyclodextrin or its derivatives as an emulsifier. Namely, Japanese Unexamined Patent Publication No. Sho 58-58139 discloses the technique of emulsification by the specific process that cyclodextrin is used by combination with oil soluble surfactant. Also, Japanese Unexamined Patent Publication No. Sho 63-194726 discloses the technique which is used methylated .beta.-cyclodextrin as an assistant emulsifier.
However, the problems such as skin irritation has not solved completely, since conventional surfactants are used by combining in these techniques.
In order to solve these problems, as for the example which is obtained the emulsion cosmetics without using any surfactant, the content in Japanese Unexamined Patent Publication No. Hei 3-284611 and U.S. Pat. No. 5,447,920 are listed. Japanese Unexamined Patent Publication No. Hei 3-284611 discloses a cosmetic comprising a hydroxyalkylated cyclodextrin, oil and water. U.S. Pat. No. 5,447,920 discloses a liquid or powdery cosmetic composition which comprises an inclusion product with a hydroxyalkylated cyclodextrin formulated therein. The cosmetic containing the hydroxyalkylated cyclodextrin is described as having improved product characteristics such as useability and stability, and effectively preventing skin roughening.
However, although hydroxyalkylated cyclodextrin demonstrates excellent solubility in hydrophilic solvents such as water, it does not do well in emulsion cosmetics primarily due to hydroxyalkylated cyclodextrin's lack of solubility in nonpolar group such as oils. In other words, a cosmetic containing hydroxyalkylated cyclodextrin displays insufficient water-holding capacity for keeping the moisture if the cosmetics contain substantial amount of oils (e.g., a water-in-oil type of cosmetics).
Thereupon, it has been developed the techniques used a hydroxyalkylated cyclodextrin which is effectively functioned to the composition as a hydrous stabilizer at the same time as an emulsifier.
However, in the water-holding of lipstick, and the like by using these techniques, the water-holding under the severe conditions such that is left for a long period of time and at 90.degree. C. in the preparation time, is still insufficient. It sometimes occurs the aggregation of coloring agent and separate into a water phase and an oil phase or an emulsion phase, it is desired the further improvement.